(1) Field of the Invention:
The present invention relates to a novel composite sintered compact containing high density boron nitride, which consists of zincblende-type boron nitride, wurtzite-type boron nitride, ceramic material and metal, is adapted for cutting hard metal and can be easily worked into a cutting tool.
(2) Description of the Prior Art:
High density boron nitride (high pressure phase boron nitride) includes zincblende-type boron nitride (hereinafter, abbreviated as Z-BN) belonging to the cubic system and wurtzite-type boron nitride (hereinafter, abbreviated as W-BN) belonging to the hexagonal system. These zincblende- and wurtzite-type boron nitrides have substantially equal density, which is about 40% higher than the density of graphite-type boron nitride (hereinafter, abbreviated as g-BN), which is low density boron nitride (low pressure phase boron nitride), and have a dense atomic arrangement.
Further, these two high density boron nitrides have high hardness, high thermal conductivity, high chemical stability against transition metals, such as iron, nickel and the like, and other excellent physical properties. Therefore, these boron nitrides are used as a material for tools used in the precision working, and a sintered compact produced by bonding Z-BN crystal grains with metal consisting mainly of cobalt and a sintered compact of a mixture of Z-BN crystal grains and ceramic material, such as titanium nitride, titanium carbide or the like, are commercially sold as a material for cutting tools at present. Further, there are known a sintered compact of a mixture of W-BN and Z-BN, (Japanese Patent Laid-Open Application No. 125,412/74) a sintered compact of a mixture of W-BN and ceramic material, (Japanese Patent Laid-Open Application No. 44,014/74) and a sintered compact of a mixture of W-BN anc metal (Japanese Patent Laid-Open Application No. 44,015/74).
Composite sintered compacts produced from Z-BN and metal or ceramic material have a very high hardness. Therefore, it is very difficult to work the composite sintered compacts themselves into cutting tools. The use of such composite sintered compacts consisting mainly of Z-BN is disadvantageous for commercial purpose when the substances to be cut are not so hard and a cutting tool having a particularly high hardness is not required for cutting the substances.
The inventors have made various investigations with respect to a method of producing a composite sintered compact consisting of a boron nitride mixture of Z-BN and W-BN, and a cermet consisting of ceramic material and metal, and to the properties thereof, and found out that the composite sintered compact exhibits excellent properties in a certain combination of the components.